Back in my day, you either worked together with others or you didn't accomplish jack shit.
The memory of your day is very different from the memory of my day, then. I remember the old days of MUDs, where I would multiclient an entire team because it was impossible to get anything done otherwise as others were entirely useless. I remember when i would effectively have to singlehandedly kill an entire enemy team by myself simply because everyone else was either Missing or Entirely Useless. The simple math dictates the relative impossibility of assembling a sizeable group of players.
Imagine a group of 5 people. Let's run some numbers
First, let's imagine 5 of those people are like me: Utterly no life insomniacs with nothing much to do: 90% uptime. Since for the action to occur, all 5 members must be up, we get 0.9^5 = 59% uptime. This doesnt' seem too bad, a group that can mobilize for action nearly 60% of the time is good for maybe 14hours a day. Now let's move down the list.
Case 2: Lifeless turbo-nerds. 67% uptime. Total uptime: 0.67^5 = 13%. They can put together maybe a 3 hour run. Not terrible, but it's clearly getting pretty hard to pull shit together.
Case 3: Work Hard, Play Hard: 8 hours of work, 8 hours in game, 8 hours dead. 33% uptime. Total uptime: 0.33^5 = 0.3% Yeah, it quickly drops off a cliff. If your group consists of people with jobs, bu are otherwise dedicated to the game, they have a less than 6 minute attention span as a 5-man unit. If it takes longer than 6 minutes, it isn't happening.
I don't think I need to do the math for groups of people less dedicated to the craft with even lower uptimes, since they'll have uptimes measured in fractions of seconds.
The whole genre's past its prime now and slipping into obscurity. Realistically, it's probably for the best; they're a huge fucking waste of time, are a catalyst for addictive behaviors, and there are better ways to be social.
Nah, I see these things going in cycles. Remember when the age of 4X was in decline, and there hadn't been anything new since Civ, and then in recent years, we suddenly get a flood of the damn things? The people who want to play these things aren't going anywhere, and if the market shifts too far away from them, eventually someone will put out something that does a good job catering to this niche and there will be a sudden resurgence.